When i was in school i took a class called Public Health and the Built Environment. My professor Dr. McMillan often rode the #3 bus to school had a whole class day devoted to social capital. That day she told us of an encounter she had on the bus one day of a lady who was lacking enough change to get on the bus (In Austin it's still 50 cents). Obviously anyone that was standing there with the woman would give her the extra change she needed to get on the bus and its telling of the generosity of Austinites that her ride was paid for through the kindness of strangers.
But when does this type of kind interaction happen in your automobile? Sure you let people cut in front of you in a traffic jam, or you might let a pedestrian go in front of you but as a personal observation it seems like one never gets to truly interact with people like on transit. Some folks don't want to be bothered by people of different social status' whether higher, lower or even student but i think it allows people to be more able to empathize with life situations and stages. Younger folks learn how to give seats to their elders and older folks might find from looking at the kids that its a great idea to bring an ipod when in transit. Taking transit might be good for the environment and good for your pocketbook but it seems like it also might be good for your conscience.